The next generation of high performance electronic packages will place emphasis on increasing packaging and thermal densities, improving reliability, and reducing weight. High performance electronics subsystems and systems will continue to incorporate increasing quantities of monolithic microwave integrated circuits (MMIC's) and application specific integrated circuits (ASIC's). Such high performance microelectronic packages including multichip modules (MCM's) will create thermal management challenges for the electronic package designer.
Conventional materials used heretofore in manufacture of microelectronics packaging include aluminum, Kovar, molybdenum, and copper-molybdenum-copper. For example, Kovar microelectronic packages comprise a Kovar housing and Kovar feedthrough pin or wire material and glass seals between the housing and feedthroughs. The coefficient of thermal expansion (CTE) of the sealing glass and the Kovar components are matched to provide a hermetic seal. Moreover, the sealing glass is selected to melt below the critical temperature for the Kovar feedthrough material. A critical transgranular and intergranular oxide are formed and controlled to create the final hermetic seal.
However, such conventional package housing materials do not meet today's high performance system requirements such as a low coefficient of thermal expansion, high thermal conductivity, high stiffness and low density. As a result, composite materials have been proposed in an attempt to meet these high performance system requirements. For example, graphite-aluminum metal matrix composite (MMC) materials meet these requirements from the standpoint of exhibiting a weight savings of 65% when used in lieu of conventional Kovar as the package housing material. Moreover, graphite-aluminum MMC materials exhibit a thermal conductivity that is six to ten times greater than that of Kovar material and can be produced by relatively low cost casting operations to shapes that are readily machinable.
In order to utilize the full potential of graphite-aluminum MMC materials for electronic packaging, there is a need to provide a reliable, low leak rate (hermetic) seal between the graphite-aluminum MMC material and the electrical feedthroughs.